Ultrasonic transducer shielding



Jan. 13, 1970 LE ROY KOPEL ET AL 3,489,932

ULTRASONIC TRANSDUCER SHIELDING Filed June 27, 1967 INVENTORS LEROY A. KOPEI.

STANLEY E. MC CARTHY ROBERT L. STETTINER smmq fi j ATTORN EY United States Patent 3,489,932 ULTRASONIC TRANSDUCER SHIELDING LeRoy A. Kopel, Cambridge, Stanley E. McCarthy,

Concord, and Robert L. Stettiner, Lexington, Mass.,

assignors to Hewlett-Packard Company, Palo Alto,

Calif., a corporation of California Filed June 27, 1967, Ser. No. 649,243 Int. Cl. H04r 17/00 U.S. Cl. 310--9.1 1 Claim ABSTRACT OF THE DISCLOSURE An ultrasonic transducer provided with electromagnetic shielding by surrounding the transducer assembly with a grounded conductor. Reduced capacitive coupling between the grounded conductor and the transducer is achieved by placing a dielectric spacer between the transducer assembly and the shield.

While using ultrasonic transducers as impulse-receiving instruments, there is a good deal of background noise, primarily from 60 cycle current and radio frequency interference. As a result of this interference, transducer reception is impaired. This interference must either be tolerated or must be compensated for by increasing the magnitude of the initial signal to be detected with the transducer.

It is the principal object of this invention to reduce the background noise in ultrasonic transducers and therefore to improve transducer reception. This is accomplished, as indicated in the illustrated embodiment of this invention, by surrounding the transducer assembly with a grounded conductor.

It is a further object of this invention to improve the signal output of an ultrasonic transducer .by limiting capacitance coupling between the transducer piezoelectric element With its damping block and the conductive shield. This is accomplished by providing a dielectric spacer between these elements.

Referring now to the drawing, which is a sectional view illustrating the preferred embodiment of this invention, there is shown a conductive shield 1. Inside shield 1 there is a piezoelectric element 2, and its associated damping block 3. The shield 1, covering at least the front and sides of the piezoelectric element, is constructed of a conductive material, is grounded by wire 4, and is insulated from the piezoelectric element 2. This insulation can be accomplished by anodizing the interior of the conductive shield.

A dielectric spacer 5 is located between the piezoelectric element 2 with its damping block 3 and the conductive shield 1. This limits the capacitance coupling which occurs between the piezoelectric element with its damping block and the conductive shield as a result of the addition of the electromagnetic shield. The units are maintained in their respective positions through the use of an insulating epoxy. The transducer leads 6 and the shield ground wire now form a three-wire system extending from the back of the ultrasonic transducer unit.

We claim:

1. An eIectro-acoustic transducer for ultrasonic energy detection systems and the like, comprising:

a piezoelectric element having front and back surfaces;

a block of damping material joined to said back surface of the piezoelectric element;

first and second electrical conductors coupled respectively to said front and back surfaces of the piezoelectric element;

a conductive shield positioned in front of the piezoelectric element and around said element, its mountings and contacts, said conductive shield having an interior surface which is anodized to form a thin dielectric layer for insulating said conductive shield from the piezoelectric element; and

a third electrical conductor coupled to said conductive shield for grounding said shield, said third electrical conductor being electrically isolated from said first and second electrical conductors.

References Cited UNITED STATES PATENTS 3,387,149 6/1968 Young 3 l08.5 3,239,696 3/1966 Burnhalter et al. 310 3.3 X 3,120,622 2/1964 Dranetz et a1. 3l08.2X 3,098,163 7/1963 'Bliss 310-8] X 2,735,024 2/1956 Kulcsar 310-8.3

OTHER REFERENCES Handbook of Piezoelectric Crystals for Radio Equipment Designers, J. P. Buchanan, December 1954, pp. 364-5 and 410-11.

MILTON O. HIRSHFIELD, Primary Examiner M. O. BUDD, Assistant Examiner U.S. Cl. X.R. 

